A video is made up of plural frames, each frame being a still image, the effect of showing consecutive frames being to give the impression of movement. The frame rate of videos is generally sufficiently high such that a viewer cannot perceive the individual frames but rather perceives a continuous moving image.
On some television displays it is desirable to increase the frame rate from that at which the video being displayed was originally captured. This can be due to increase frame rate requirement for display in accordance with a different standard from that at which the video was captured.
In addition, many of the latest high-performance television sets, particularly large screen and wide screen (16:9 format) versions, use a 100 Hz screen refresh rate instead of the conventional 50 Hz refresh rate. This is primarily to avoid screen flicker, which becomes more perceptible and annoying to the viewer as the screen size increases. However, standard television broadcast transmissions only contain 50 frames per second. Therefore if television is being watched on one of the latest high-performance television sets, the frame rate must somehow be doubled.
Such increase in frame rate is referred to as frame rate up-conversion. Frame rate up-conversion is used to eliminate large areas flicker on a television screen. Motion judder is a problem that can arise in such situations with some types of up-conversion that are currently used.
While up-converting, i.e. subjecting a video to up-conversion, new interpolated frames are added to the original or source video stream. Typically, one interpolated frame is determined and added temporally between two existing frames. A known method for achieving this up-conversion or frame interpolation is to show each original frame twice. This is an acceptable solution in static regions but problems occur in moving areas of the displayed video. The problems are referred to as “motion judder” and blur and they cause degradation in visual quality which is undesirable.
One known method for frame interpolation is described in the paper entitled Real-time 2-3 Pull-Down Elimination Applying Motion Estimation/Compensation In A programmable Device, by R. J. Schutten and G. de Hann of Philips Research Laboratories, Eindhoven, the Netherlands. In this document a method of frame interpolation is described in which motion estimation is utilized to enable judder-free display of movie material. The method described utilizes a complex algorithm by which motion estimation is achieved by sub-sampling original frames from a video to be up-converted.
The motion of an object in the frame is described using a simple translational model and parameters are then estimated for the model to obtain a useful description for an object in the image. The motion parameters are then selected from a number of identified candidates based on a cost-function analysis. Last, segmentation occurs. This is described as an extremely important step in the algorithm. Its task is to assign one motion model to each group of pixels. This is achieved by assigning the best matching model to each group of pixels, which is typically as large as 8×8 pixels.
The algorithm is extremely complex and expensive computationally.
US-A-2003/0194151 discloses a method of temporal interpolation of an image sequence using object-based image analysis. The method comprises the steps of image segmentation for partitioning a known image into objects, motion estimation, object-based motion field processing, determination of object depth order and graceful degradation for alleviating visible artifacts.